The invention relates to electromagnetic brakes and clutches having an energization coil energizable to attract an armature to a magnet body for starting or stopping a rotating member, and more particularly to a detector sensing engagement of the armature and the magnet body.
Mechanical engagement sensors for electromagnetic brakes and clutches are known in the prior art. These sensors typically include a series of three mechanical switches arranged in a generally triangular pattern around an armature and sensing closing movement of the armature. Heavy duty switches are required, to withstand the closing action of the armature, which robust construction increases cost. Furthermore, a machining operation is typically required to afford the necessary precise mounting location of the switches, further increasing cost. Alignment must also be precisely controlled so that all three switches close simultaneously. The tolerances are quite narrow and unforgiving because even a small magnetic gap substantially increases magnetic reluctance.
Another approach in the prior art is the use of an inductive proximity switch sensing closing movement of the armature. The above noted limitations also apply to such switches.
The present invention provides electronic detection circuitry, eliminating reliance upon prior mechanical or proximity switches. The present invention provides a significantly lower cost alternative to the prior art. In the present invention, the detector, or proving switch, may be located remotely from the brake or clutch, with no additional wiring to the brake or clutch being required. The invention may be used with a wide variety of power transmission devices, with no need for tuning to the specific power transmission device as in the prior art, e.g. machining, etc. A further advantage of the present invention not obtainable in the prior art is use with power transmission devices too small in physical size to use the above described approaches involving mechanical or proximity switches.